1. Field of the Invention
This invention relates generally to improvements in a hydraulically-actuated control device for controlling an operation unit including seat and backrest in a treatment chair and the like in an interlocking relation with reciprocating movement of a hydraulic piston, and more particularly to a hydraulically-activated device for controlling an operation unit including a seat and backrest in a treatment chair and the like with an interlocking relation with reciprocating movement of a hydraulic piston.
2. Prior Art
In recent years there has widely been used a treatment chair or the like whose operation unit (hereinafter referred to as "an operation unit") such as a tilting backrest 101, a vertically movable seat 102 as shown in FIG. 1 is controlled by hydraulic operation.
However, control of the operation unit in the hydraulically-actuated control device used in the treatment chair of the kind described is effected by turning on and off flow of oil through a hydraulic passage by operating a magnetic valve quick in closing & opening operation (several milliseconds of several tens of milliseconds) as for example shown in FIG. 2. The structure shown is of a normally closed type and is designed to open and close the valve and flow oil from an inlet port 51 to an outlet port 52 by moving up and down a valve body 54 which is a movable core depressed normally by a spring 55 of a cover plug 53 by energizing an electromagnetic coil 57, and accordingly when the operation unit starts and stops operation, it is impossible to prevent momentally shock produced in such starting and stopping, which means a patient on chair feel uncomfortable, and in some extreme cases, affects him adversely. This is a disadvantage.